brake bleeding query (non nova, mini)

[John]

My mates bmw mini failed it's mot on corroded rear brake pipes. We have replaced the front to rear brake pipes and bled as normal. Since doing this the pedal is almost at the floor when it brakes. It will bring the car to a halt and lock all four wheel when on a jack. We've bled the brakes twice, and can't get any air out? if you pump the pedal quickly it will come back, but only for a split second. I am right in thinking i may possibly have a servo fault? Any-one had similar experiences?

[16v Nova Kev]

sounds like the master cylinder to me john

[John]

sounds like the master cylinder to me john

why'd you think that kev?

[Pistol Pete]

Servo could be borked?? Any leaks at all?

[16v Nova Kev]

it might have reversed a seal when bleeding them. just going on the pumping the pedal up then loosing the pedal after that.

[John]

No fluid leaks whatsever, we've checked and re-checked. I used my mini flarer and made a join where there wasn't one before, on both pipes. The rears lock and release fine with the pedal.

[MK999]

I'd say it was MC too.

The only 'adjustable/moving' connections between the pedal itself and the calipers (assuming a good bleed) are the caliper/pad auto adjustment, which I assume you didn't change but may have knocked or introduced a fault during removal/refitting somehow, the linkage, which would be odd to change it's setting (unless it's something like the nova one which has a couple hundred points of possible failure lol) and lastly, the MC which operates outside of it's normal conditions while bleeding brakes.

[16v Nova Kev]

^:thumb: .
nowt to do with a servo. imo

[John]

I'd say it was MC too.

The only 'adjustable/moving' connections between the pedal itself and the calipers (assuming a good bleed) are the caliper/pad auto adjustment, which I assume you didn't change but may have knocked or introduced a fault during removal/refitting somehow, the linkage, which would be odd to change it's setting (unless it's something like the nova one which has a couple hundred points of possible failure lol) and lastly, the MC which operates outside of it's normal conditions while bleeding brakes.

what? lol

I've just been and re-bled the brakes twice, and it's still exactly the same. Bled 0.5 litre out of each corner, and no air whatsoever. The thing i can't understand is the pedal feel returns if you pump it up, but has dropped off the next time you press it, would this happen with a fooked m/c? I'm hoping it's not the servo as it looks a fooking nightmare to replace lol.

[John]

rep left where i can :)

[scottish]

master cyl

[16v Nova Kev]

100% m/c just changed one on a hyd clutch.pump it up you got a pedal then if you left it 30secs the pedal just went to the floor.

[MK999]

Surely the servo is bolted onto the MC, making the MC about 4 bolts 'harder' to replace as you'll have the servo out anyway?

Basically something which either moves for adjustment or auto adjusts is doing so wrongly as you're getting normal braking action but far further down the pedal movement. These are, the MC and it's clever seals which draw fluid into it to keep it full without losing pressure when it moves, the linkage which is adjustable to set the pedal in the correct place, and the pad wear adjustment. NOTHING else is between the pedal and the brake disc to change the point at which, through the brake travel, the pad hits the disc!

The servo simply assists the MC, and you only get odd happenings with those when the seals or one way valve are entirely fooked and it sucks the pedal straight to the floor without doing anything etc.

Out of all of those, pad wear adjustment is hard to change unless you're changing the pads etc (This is those weird shape springs on ATE's) The linkage is even harder to accidentally move, that leaves the MC which is operating outside of it's normal conditions. i.e moving larger amounts of fluid while creating no pressure, and having this pressure released often resulting in a flow of fluid and a resulting negative line pressure.

Hope that clears it up.

[John]

I will try and see if i can get one tommorow and get it fitted.

[John]

Surely the servo is bolted onto the MC, making the MC about 4 bolts 'harder' to replace as you'll have the servo out anyway?

Basically something which either moves for adjustment or auto adjusts is doing so wrongly as you're getting normal braking action but far further down the pedal movement. These are, the MC and it's clever seals which draw fluid into it to keep it full without losing pressure when it moves, the linkage which is adjustable to set the pedal in the correct place, and the pad wear adjustment. NOTHING else is between the pedal and the brake disc to change the point at which, through the brake travel, the pad hits the disc!

The servo simply assists the MC, and you only get odd happenings with those when the seals or one way valve are entirely fooked and it sucks the pedal straight to the floor without doing anything etc.

Out of all of those, pad wear adjustment is hard to change unless you're changing the pads etc (This is those weird shape springs on ATE's) The linkage is even harder to accidentally move, that leaves the MC which is operating outside of it's normal conditions. i.e moving larger amounts of fluid while creating no pressure, and having this pressure released often resulting in a flow of fluid and a resulting negative line pressure.

Hope that clears it up.

yes understanding now, thankyou muchly. :) (took a couple of reads, it is 22.47 on friday night lol) Makes sense actually because the servo was/is fine before m/c opened/bled.

[marc69]

had probs with minis brakes before, the air seems to go up far in the system, you will have to almost put all new fluid through the whole system, takes ages....be patient!

[MK999]

(took a couple of reads, it is 22.47 on friday night lol)
I've been without the internet, and therefore PNG for a few days as some numpty crashed square into the phoneline cabinet outside my house at uni and totally destroyed it, but I have had plenty of work to do and a bit of motorsport news to catch up on with possible interviews looming... Basically it's all written in "Engineering Report" and I can't really help it lol

[John]

looking at it, the abs pipework is almost higher then the fluid resevoir, we cracked the pipes off at the abs pump to eliminate trapped air, but nothing. Lets hope it's the m/c

[MK999]

I didn't factor in ABS/the mini 'CAN' loom, could be anything from the MC to an indicator bulb or damp carpet then lol

[John]

The thing is, the brakes were fine till i've done the pipes, so it's gotta be related surely?

[16v Nova Kev]

sounds like it bud

[MK999]

The thing is, the brakes were fine till i've done the pipes, so it's gotta be related surely?

99% yeah, I was having a jab at overcomplicated modern cars and BMW's 2.5 tonne idea of a 3-4 wires to run everything system/philosophy. This obviously missed you entirely after a long day lol

[John]

99% yeah, I was having a jab at overcomplicated modern cars and BMW's 2.5 tonne idea of a 3-4 wires to run everything system/philosophy. This obviously missed you entirely after a long day lol

Pmsl , yeah it deffo went over my head lol lol

[autoworksnovasport]

is this the new mini or the good one (rover mini) how is the system set up corner to corner or fronts and backs??? if its the older mini the m/c sits straight up and air bubbles sit at the top of this cylinder best was is to use a presure bleeder and get some one to pump pedal aswell if needed

[John]

is this the new mini or the good one (rover mini) how is the system set up corner to corner or fronts and backs??? if its the older mini the m/c sits straight up and air bubbles sit at the top of this cylinder best was is to use a presure bleeder and get some one to pump pedal aswell if needed

Bmw (shoite) mini.

[MK999]

*Maxi. lol

[autoworksnovasport]

Bmw (shoite) mini.

bmw bit different then id still use same method though :thumb: